An automatic transmission uses frictional engagement elements to connect and disconnect driving force transmission from a driving force source. When a frictional engagement element is controlled from a disengaged condition to an engaged condition, the frictional engagement element may vibrate, and this phenomenon is known as judder. Judder may cause a driver to experience discomfort and unease, and therefore control is conventionally performed to prevent judder from occurring.
Judder becomes steadily more likely to occur as input torque input into the frictional engagement element increases, and therefore JP2010-196810A discloses control for reducing a driving force of an engine serving as the driving force source when judder occurs.